I feel like this is a cake˛ solution.
One of the things the Dresden Verse is big on is choice, and if you have a limited resource you are paying your spells from, that's an excellent way to get that across when it comes to wizards. Either do the spell and make it count, or don't. Harry often opens with a big blast of fire, if necessary, and if that doesn't work, he either runs or he gets creative. If instead, you just spend all your available spells trying to get that one lucky hit, you don't really use them to their best potential.
If you want to extend the amount you can cast, there are already plenty of options. You can take Enchanted Items. 1 Point of Refresh can give you 8 additional spells if you put them all on 1 item to increase uses per session. Sure, they are not flexible, but spread them around and you're golden. Or take one or two points in frequency specialization, and it'll get you even more.
Or you can take breath weapon as a way to emulate your talent and/or training for combat magic. You can slug those out pretty much as much as you like, without them costing stress.
But with both those options, you still make a choice. You are spending your refresh, again a limited resource, that you could spend on other upgrades instead. If this is a way to get around having to take, for example, the "guns" skill, I feel like it is again cheating the choices the game forces you into. I think it's better to either get creative with the spells you do have, or concede to fight another day.